Question

To be able to read data from compressed blocks, Cassandra consults __________.

a) Commit Log
b) Memtable
c) Bloom Filter
d) SSTable Index

Answer 1

Cassandra uses the Bloom Filter to quickly check if a row key might be in an SSTable, thus saving I/O operations before consulting the SSTable Index for the exact data location.

Step-by-step explanation:

When reading data from compressed blocks in Cassandra, the system consults the Bloom Filter before it looks into SSTables. The Bloom Filter is a probabilistic data structure that efficiently tests whether an element is a member of a set. In Cassandra, Bloom Filters are used to quickly determine if a row key is present in an SSTable without having to read the file, thus saving on I/O operations. If the Bloom Filter indicates the row key might be in the SSTable, Cassandra then utilizes the SSTable Index to locate the exact position of the row within the SSTable for retrieval.